This comic is essentially a set up for a pun: "Underground" can mean "under the ground" (buried in the dirt) or "non-mainstream." In this case, Ponytail is whining that she had been doing paleontology before Jurassic Park kicked paleontology into the mainstream with living reproductions of dinosaurs, thus apparently undermining the hard work paleontologists had done. In other words, this comic is also poking fun at hipsters.

Of note is the fact that Acrocanthosaurus is misspelled in the third panel as "arcocanthosaur." Assuming this isn't merely a spelling mistake on Randall's part, Ponytail's incorrect pronunciation further undermines her self-proclaimed superiority over all the Jurassic Park-inspired "bandwagon" paleontologists.

The title text refers to both the phenomenon called 'jumping the shark' and the controversy having the Brontosaurus's scientific name changed to Apatosaurus, despite that Brontosaurus had already made a name for itself in the mainstream. 636: Brontosaurus also references the Brontosaurus name change. An Apatosaurus also appears in 15: Just Alerting You, and 650: Nowhere. Ichthyosaurs are marine reptiles with bodies resembling sharks or dolphins, which lived alongside dinosaurs during the Mesozoic era.

Another interpretation: Both 'brats' have taken Jurassic Park literally and not as a fantasy story. So "under ground" refers to them, that the dinosaurs of Jurassic Park would have been there indeed and not only in fantasy.